Tuning inductor



Aug. 5, 1952 D. R. DE TAR 2,605,315

TUNING INDUCTOR Filed Aug. 5, 1948 5 Sheets-Sheet 1 /HIGH 7.' [4 BAND 0 .2 .4 .e .a 1.0 r2 m 1.6

SLEEVE MOVEMENT (INCHES) he T E (3%) D. R. DE TAR TUNING INDUCTOR Aug. 5, 1952 3 Sheets-Sheet 2 Filed Aug. 5, 1948 Aug. 5, 1952 D. R. DE TAR 2,606,315

TUNING INDUCTOR Filed Aug. 5, 1948 3 Sheets-Sheet 3 Patented Aug. 5, 1952 UNITED STATES rarest or F I- CE T UNING INDUCTOR 'D na1k1Jit. -D Tar, Stratfor'd, 001111., aSSig'noi-"t'o Aladdin Industries, Incorporated, Chicago, 111., acor'poration'of Illinois Application August' 5, 1948, Serial No. 42,608

'Myin'venti'on relates to an improvedtu'ning inductor particularly suitable for 'use'at veryhigh radio frequencies.

Tuning inductors employingmo'vable plungers -such' as mag-netic'me'mbers or low-loss conducting members, are particularly desirable-at very- '-high' frequencies where circuit geometry is espe- 'cially important-andvariable tuning capacitors 'intro duce serious problems of circuit arrangement. I-Iowev'erQthe use oi these tuning inductors in'the very-highfrequencyrange has heretofore been impractical because of the very small *mechanical movements associated with large variations of frequency and the consequent requirement of precision plunger-moving devices "without lost motion or backlash.

In "accordance with the present inventionthe "problems of circuit geometry-and aohieving precision mechanical "movements heretofore associated with the use of'tuning-plungers in the'veryhigh" frequency tuning ranges 'are overcome by formingthe inductance in the shape -of'-an-elongated U. I'he-movab1e-plunger is of elongated -'sha'pe capable of "being "received betwee'n the "parallel leg members of theU-s'haped'coil andis shifted in direction at right angles to the mag- "neticaxis-the'reof to achieve the inductance variations requisite to tuning. Furtherin accord- "an'ee with the present invention, two or more turns" maybe formedin' the elongated U shaped coil 'by connecting bridge members'between a plurality of vparallelconducting -members. The fb'ridgemember atone end of'the coil are shaped to define "a 'cylinderdn'conjunotion with the parallel conductingmembers' and thereby'permit insertion of the tuning plunger for telescoping "movements'relative to the 'leg'portions' of the coil. tuning "inductor having features in common "with "the present invention is described and claimed in my co-pending application, S. N. 42,667, entitled -Sleeve Tuner, filed August ,5, 1948, now abandoned.

. --It is,--therefore,"a; general-object of the. present inventionto provide an improved :tuning inductor --tunable o'ver a-wide very-highfrequency'band by movement of a tuning plunger over a relatively great distance to provide" fine frequency adj ust- "'inentwithout the precision rhe'ch'anical struc- ""ture heretofore'required for this-purpose.

Another. object of the present invention is to provide animproved tuning inductor embodying afsmall Il-iimber oi'turns' afid sliitable for use at "very-high radio frequencies and in which atun- V lng plungermovable along an axis transverse to "2 the magnetic axis ofthecoil defined thereby'is provided.

Further it is-an object of the present invention to providean improved tuning in'ductor capable "of tunin over a wide very-high frequency band with substantially constant "Q.

My invention further residesin providing an improved tuning inductor capable of fficiently tuning over a wide very high frequency band and which embodies features of construction, combination and arrangement rendering it simple, rugged in construction,. andof small size to the end that it may-be usedin a wide range of applications in radio I equipment.

The novel features which-I believeto be characteristic of my invention are set forth with particularity in the appendedclaims. MyTinven'tion itself, however, may best be understoodbyre'ference to the followingdescription taken in connection with the accompanying drawing in which,

Figure l is a side elevational viewwith parts broken away of one embodiment of "the present through the axes 9-9,-and l0l0, Figure S, respectively;

"Figure 11 is a side elevational view-withparts in cross-section of yet another embodiment of the present invention;

Figure 12 isa cross-sectional view of the structure of Figure 11 through axis l2-I2;

Figure 13 is a cross-sectional view-through the axis l3--l3, Figure 12; and

' Figure 14 is a cross-sectional view through axis 'Referring now toFigures 1, 2, and 3, there is shown at 20 a conducting ribbon of copper or like material and which is snugly received in the substantially annular space between the nonconducting tubes 21 and22. The leg portions 202 and zflb'of ribbon 20 extend upthis annular sulating base 24 to which it is attached by a plug 25 snugly received in the bottom of tube 2| and in a suitable hole in base 24. This attachment may be achieved in any one of many other ways known to the art.

The legs a and 2612, together with ring 23, define a cylinder having an axis midway between these legs and extending in the direction thereof. The lengthy magnetizable core 26 is mounted concentrically with the axis of this cylinder as indicated in the figures.

Core 26 is sustained within tube 2| by the resilient wire 28a which is molded in the bottom portion thereof and extends downwardly as shown in the broken away portion of Figure 1. This wire is held at its lower end by the solder ball which is received on the rivet-like sleeve 25. The latter sleeve is snugly received in the opening in base 24 provided therefore and thus holds the core relative thereto. This sleeve also snugly receives the tube 2| to hold that tube in position relative to the base 24.

Sleeve 22a of insulating materia1 is interposed between the base 24 and the outer sleeve 22.

The core 26 comprises a suspension of comminuted magnetic material in a non-conducting plastic binder, such as a phenolic resin. This material is characterized by relatively good magnetic permeability as compared with the air and by relatively low power losses, even at high radio frequencies.

The core 26 define paths for magnetic flux encircling the elongated U-shaped coil defined by conductor 20 and thereby increases the inductance thereof beyond the inductance otherwise achieved.

A low-loss conducting sleeve 28 is interposed between the core 26 and the inner tube 2|. This sleeve is made of copper or like material and has an upper end wall which receives the supporting shaft, 30. This shaft is threaded to be received in a suitably threaded opening provided in yoke 32 to secure the leeve 28 to yoke 32 by an adjustable connection.

Means (not shown) are provided to shift yoke 532 in the direction of the axes of tubes 2| and 122 and thereby telescope sleeve 23 to a greater or lesser degree within these tubes. If desired, a plurality of sleeves 28 are moved in unison by a common yoke 32 to achieve tracked tuning of a plurality of tuned circuits.

Suitable indicator means (not shown) calibrated in terms of frequency or Wavelength is preferably provided to indicate the position of sleeve 25 in terms of the resonant frequency of the tuned circuit.

The effect of alternating current flow through the elongated U-shaped coil defined by conductor 26 is to induce eddy current flow in the sleeve 28. The resultant eddy currents are in direction, magnitude, and phase to overcome the magnetizing effects of the current flow in the coil, thereby creating a field free space within sleeve 28. Since this field free space is unavailable for magnetic flux lines encircling the conductor 28, the inthe legs 20d and 20e.

4 ductance thereof is decreased to the extent the sleeve 28 is telescoped within the cylinder defined by that conductor.

The sleeve 28 also progressively encircles the core 26 as it is shifted within the coil defined by conductor 26. This reduces the effect of that core in contributing to the inductance of the coil and, in addition, substitutes its power losses for the power losses otherwise associated with the time varying magnetic field within core 26. This vari ation in losses may be chosen to make the resultant inductance act as if having internal resistance in proportion to its reactance and hence to appear to have a constant value of Q.

Figure 4 shows the results of tests on an inductor of the type shown in Figure 1 and having the following dimensions:

Sleeve 28-copper, 0.25" and 0.205" outside and inside diameters, respectively;

Conductor 2Uflexible copper strap with legs 20a and 20b, 0.21 Wide and 0.005" thick and 1% high;

Core 260.200 diameter.

It will be evident from curve A that the Q of the inductance remains constant within about 9 percent over the entire 175.25 to 211.25 me. high frequency television band. Moreover, as shown incurve B, the tuning curve is very nearly a straight line within this frequency band.

The actual sleeve movement shown in Figure 4 is approximately 1.3 inches for the television band shown. This degree of movement is ample to permit adjustment of the inductor to any television station within this band without requiring a special precision mechanism having no backlash or lost motion. Thus, simple and inexpensive mechanism may be provided to shift yoke 32 without losing the desirable characteristics of accurate and reproduoeable tuning.

Figures 5, 6, and 7 are like Figures 1, 2, and 3, respectively, but the core 26 is moved to achieve tuning and sleeve 28 is omitted. Since movement of the tuning plunger defined by core 26 causes the flux encircling the conductor 20 to vary, tuning action is achieved as that core is shifted to a greater or lesser telescoping relation with the tubes 2| and 22.

In the structure of Figures 8 to 10, the conductor 23 defines two turns of elongated U-shape configuration. As shown, this conductor defines a plurality of parallel leg portions 2&0, 2M, 20c and 20f which form the elements of the cylinder defined by the annular space between tubes 2| and 22. A lower bridging member 299 connects Upper bridging members 23a and 23b, in the shape of segments of the cylinder defined by tube 2|, connect the legs 20c and 20c and 20d and EM, respectively, thereby defining a two-turn winding when the conducting path is traced from one end of conductor 26 to the other. The magnetic axis of this winding is transverse the axes of tubes 2| and 22.

The sleeve 28 acts as a tuning plunger to vary the inductance of the two turn coil of Figures .8 to 10 in accord with the degree to which it telescopes that coil.

It will be observed that the bridging members 23a and 232) form segments of the cylinder defined by the legs Zilc to 201 and thereby permit the sleeve 28 to move freely without. contacting the conducting portions of the structure. However, the bridging connection 20g extends diametrically across this cylinder since it is beyond the limit of movement of sleeve 28.

Figures 11, 12, 13, and 14 show another form of the present invention like that of Figures 8, 9, and but in which a unitary structure of the inductor and a trimmer capacitor is provided. As shown, a two turn elongated U-shaped coil is defined by the lengthy parallel conducting legs 22c, 22d, 22c, and 22,1 in conjunction with the ring 34 and the conducting segments 23a and 23b.

A conducting ring 34, Figure 11, snugly fits about the tube 22 adjacent the bottom end thereof. The bottom ends of elements 26d and Zile are soldered or otherwise attached to this ring to define a two-turn coil.

The magnetic core member 26 is supported within the tubes 21 and 22 as shown, thus defining an annular space within which the sleeve 28 telescopes.

The ends of conductor extend in directions transverse to the axes of the tubes 2| and 22 and are attached to the opposed condenser plates 36 and 38. As seen best in Figure 13, the condenser plate 36 is resilient and tends to bend upwardly to the curved condition shown, thereby providing minimum capacitance across ends of conductor 20. This tendency is adjustably overcome by the screw 42 which rides in a threaded opening in the insulating base plate 24. This screw acts against the insulating washer 49a. Moreover, an insert 42 of mica or similar lowloss dielectric material is interposed between plates 36 and 38 to prevent electrical contact between the same.

It will be evident that the structure of Figures 11 to 13 provides an inductor tunable by shifting movements of the sleeve 28 and, in addition, which is provided with a unitary trimmer condenser for adjusting the resonant frequency at any one position of sleeve 28.

In the foregoing specification and the appended claims I have used the term cylinder to define the surface generated by straight line translational movements of a two-dimensional closed surface without regard to whether that surface is a circle.

While I have referred in this specification totelescoping movements of the tuning plunger relative to the tubes 2| and 22, it will be observed that these movements also telescope the cylinder defined by the conductor 20 and the bridging member 23 or bridging members 2311 and 2312.

While I have shown specific embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto since many modifications and alternative constructions may be made without departing from the spirit and scope thereof. I intend by the appended claims to cover all such modifications and alternative constructions as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A variable inductor for use in very highfrequency circuits comprising an elongated cylindrical tube formed of insulating material, an elongated U-shaped inductance element comprising a pair of leg portions fitted snugly over said tube and defining diametrically opposed segments of a cylinder and having also a top portion surrounding said tube near one end thereof and comprising a complete circular annulus conductively joining said leg portions, a cylindrical conducting member received within said tube and adapted for telescoping movement therewith, means for slidably moving said conducting member Within said tube and outward therefrom through and beyond said annulus, whereby the portion of said conducting member oriented between said leg portions may be varied within predetermined limits, and connecting means for the respective ends of said leg portions remote from said annulus adapted to permit the elec trical connection thereto of an external circuit.

2. Apparatus according to claim 1 wherein said conducting member is hollow and having also a cylindrical core of magnetically permeable material carried within said tubing and means for anchoring said permeable core against movement relative to said leg portions.

DONALD R. DE TAR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 542,471 Golden July 9, 1895 642,859 White Feb. 6, 1900 2,106,120 Lindberg Jan. 18, 1938 2,222,387 Wheeler et al. Nov. 19, 1940 2,431,425 Sands Nov. 25, 1947 2,497,662 Dressel Feb. 14, 1950 FOREIGN PATENTS Number Country Date 230,818 Switzerland Jan. 31, 1944 254,568 Great Britain July 8, 1926 581,065 France Sept. 18 1924 

